Discussion

Project: Fixing a Vintage Carbon Chef Knife by Hand

It started off with one of those rare and surprising acts of online thoughtfulness where you are reminded that the internet consists not only of anonymous jerkwads arguing virulently and browsing for porn, but also very nice people who you'd never have met otherwise.

Months after I posted that I'd always liked vintage knives but haven't had a lot of luck finding one for a good price, Delucacheesemonger contacted me and offered to sell me a vintage knife he had spotted for a good price on ebay. He bought it with me in mind and offered it to me for what he paid for it. I accepted, and was soon in the possession of a 12 inch vintage carbon steel chef knife.

It's got a great feel to it. Smoothed over wooden handle. It's a BIG knife. Not too thin behind its edge, but I'll remedy that eventually. Nice medium soft carbon steel that sharpens quickly and takes a very nice edge. No bolster. No rust.

There is one big problem though: like most old knives that have seen a lot of use, it has not been carefully sharpened. It looks as though it has been steeled extensively, but not carefully. The result - the edge retreats noticeably in the middle of the knife. Accordion cuts would be guaranteed if I use a normal cutting motion.

So I decided to fix it. Somewhat foolishly - by hand. My method and results will follow in the next post.

Below are some pictures. You can get an idea of its size. And also of why it needed fixing.

The middle section certainly has been overground -- big time. It will take a bit time to fix it. I wonder if you should take it to a machine first, like a belt sander or something. I don't think it isn't anything you cannot fix. It may just take sometime with free hand.

I guess the main reason I post this in the first place is because I'll bet that there are others who like vintage knives as well. And if you like vintage knives, you're going to see a lot of knives with this kind of concavity in the edge profile - in fact you might see this even with your own knives - anything that has been sharpened haphazardly for years. Now, you could leave such a knife as is and just use it as a slicer, but then what's the point of going out of your way to buy cool old knives in the first place? So maybe the process I describe below will be useful to someone else. Hopefully at least the knife guys find it interesting.

So, onto fixing it. Normally this would be a job for a belt sander at the least. But my belt sander has been on the fritz, and I've been lazy about getting it fixed or replaced. My next best option - a 500 grit bester waterstone. And elbow grease.

What worked best for me: I sharpened at a super obtuse angle - maybe 40 degrees per side. The thinking is that this would speed up the regrinding and allow me to flatten out the edge as quickly as possible. Also, I wouldn't worry too much about holding a super consistent angle while reprofiling, since I'd have to completely grind in a new, low angle edge afterward anyway. At any rate, it seemed to speed up the process.

I wound up applying a lot of pressure in my strokes. One of the nicest things about a particularly hard coarse waterstone is how much pressure you can apply without too much risk of gouging the stone. It helps for big reprofiling jobs like this.

I started with the knife at an angle to the stone as I normally would while sharpening. I focused a lot of pressure and strokes on the raised parts of the edge, but made sure to give the entire edge the occasional swipe just to keep myself from creating new problems while trying to fix the big one. I switched sides every few minutes.

Once the edge started getting closer to straight, I switched my technique and started holding the knife lengthwise to the stone, so that the entire edge (except any recessed parts) touched the stone at the same time. I used this type of lengthwise swipe until the edge was straight.

Once I got the edge straight, I ground in a new edge on the left side of the knife - at a much lower ~15 degrees. I was hoping to grind in an asymmetrical bevel, so I kept on grinding long after I formed a burr. But I was getting a little tired at this point, so I gave up around 60/40 and ground in a new ~15 degree bevel in the right side of the blade as well. Ground down the shoulders of the bevels a bit (though the knife still needs a good bit of thinning behind its edge), went up to 2k grit, and finished with a one-sided microbevel.

100% better already, and very usable. Still needs a little work to get the edge geometry where I want it, but the major repair is done. Took maybe 2 hours - I watched a movie while I did it. Not a fun job, but a good learning experience, with a fine end result.

"Once the edge started getting closer to straight, I switched my technique and started holding the knife lengthwise to the stone, so that the entire edge (except any recessed parts) touched the stone at the same time"

Any reasons why you didn't start off with this first? Much like your third photo with the knife sitting on the cutting board. I would put the knife on the stone like that. Put the knife lengthwise on the stone and go back and forth to grind it until the edge profile is straight. Then, put the bevels on.

My thinking was that I couldn't apply the kind of pressure I wanted that way, or the long efficient strokes. Also, grinding in a working bevel afterward if you held the knife completely perpendicular to the stone would be a PITA - and since the edge would be much thicker in some places than others, you run the risk of accidentally grinding in a new regrind when you make that working bevel. Also seems like there would be some potential to really warp your stone doing that.

That said, that's just my speculation. I haven't tried fixing a nasty regrind ONLY holding the knife perpendicular to the stone like you suggest. So I couldn't say with certainty which method works better. But I used A LOT of pressure for most of the grinding, and i don't know that using that much localized pressure would be possible or advisable holding the knife differently.

You won't have to apply the same force when grind with the knife perpendicular to the stone. The contact area is much small, so the same force will generate greater pressure; alternatively, less force for same pressure.

Yeah, the edge will definitely be thicker in some places than the others. So that is something I had to work with and I would initially grind the bevel at an angle, but also going back and forth along entire edge. In short, definitely not sharpening the knife in sections. It also will noticeably grind the stone, but that is something to be expected and can be fixed.

"You won't have to apply the same force when grind with the knife perpendicular to the stone. The contact area is much small, so the same force will generate greater pressure; alternatively, less force for same pressure."_______Good point. Though it makes for more work when grinding in the working bevel.

"Yeah, the edge will definitely be thicker in some places than the others. So that is something I had to work with and I would initially grind the bevel at an angle, but also going back and forth along entire edge."_________I guess I'm still thinking that if I had to deal with unevenness, I'd rather do it while I'm grinding the edge flat fast, hard, and sloppy than when I'm trying to create a working bevel. Having a nice, flat primary bevel is pretty important to me, and I'm just not so sure I'd get the results I want grinding that bevel into a very unevenly thick edge. At least not without a whole lot of futzing around.

OTOH - I occasionally fix knives with smaller regrind issues for other people, so maybe I'll try your suggestion out sometime and compare. This knife just happened to be a pretty extreme example.

Excellent job Cowboy. I would have though you had a XXC DMT plate for this job although it would have taken considerable time to remove the aggressive scratch pattern left from the diamond plate. The appearance of the knife before the fix looks different from the standard Sabatier. Less upswing near the tip. Almost gyuto like. Now it looks like a sujihiki

I actually do have a big DMT xxc plate, but I save it for flattening. Also, I have a lot of faith in that Bester stone. Very little noticeable wear and tear considering it was such a big job. And it takes much better to using a lot of pressure in your stroke than a DMT does. Also, it just feels better to me than using the DMT xxc - I get sort of a nails on chalkboard thing when grinding with that plate, which would be pretty unpleasant for jobs taking well over an hour.

In a sense, it is almost a huge sujihiki now. The flat section of the knife's edge is nearly 7 inches long. Thing is it is so big that it's actually as tall as many gyutos. But I intend to use it especially for slicing. Also for scaring people.

I think you are smart to do this by hand rather than machine. (A) the grinder would take the temper out of the steel and (B) re-HT is unknown; and (C) you'd have to waste & replace the nice handle.

I would hand file this knife, one lick at a time, until you get the belly you want. You can file perpendicularly, or just drag it along the file. Alternatively, you can use a slow wheel running in a waterbath.

A hand file might have been very smart in retrospect. A job like this can put a serious hurt on a waterstone.

I'm wondering though why you'd think I'd have to replace the handle after using a belt sander? You mean because I'd have to re-heat treat it? I've pulled off some large-ish jobs on a belt sander before - it's easy to mess up a HT that way, but not impossible to keep it from happening. Just dip a knife in water after every couple passes. Slows you down, but preserves the knife, and it's still faster than reprofiling completely by hand. Of course for a big job like this, it's easy to have a moment of boredom or frustration set in and get the edge hotter than you meant to, even with precautions in place.

Yes,. it was because you'd have to remove the old handle to re-HT (It can be done without ruining the scales, if among other things, you have access to the same size cutler's rivets, and don't bugger anything up when drilling out the old ones).

And you're also right about the "dip, dip and swing" method of keeping the steel cool. This works far better when it's the whole *flat* that's being ground. When you put the edge on anything abrasive (dry) that's moving fast with any pressure at all, all it takes is a about second to get the steel glowing orange-red. At that point, you and the steel are likely cooked. Yes, you can do it that way, but I wouldn't. (If you do, keep your quench bucket right under the leading wheel of the sander and put a glop of DW liquid in it--reduces slimey mess).

Truth is you're almost certainly more practiced with a belt sander than I am. So your advice is very welcome. I've managed to use one for much smaller jobs without ruining a temper. But I don't have the same kind of confidence in my degree of focus for a job this big.

Hey, cowboy, whatever works! Frankly, I think you'd be surprised how fast a good file can put the belly back in that blade.

Ooooh, here's another idea that works--There are small *hand-cranked* stone grinders out there right now in about 50,000 garage sales. You clamp 'em to your bench, and the good ones have a gear reduction that is pretty sweet for what you're doing. I use one for shaping pieces for inlay. They stay pretty cool--at least enough that you don't have to fret over waiting a second too long before quenching. $5 should buy you the best.